1. Field of Invention
This invention relates to Group Transfer Polymerization employing supported initiators or catalysts.
2. Background
Preparation of "living" polymers by Group Transfer Polymerization (webster et al., "Group Transfer Polymerization--A New and Versatile Kind of Addition Polymerization", J. Am. Chem Soc., 105, 5706 (1983)) is well known. Group Transfer Polymerization (GTP) methods are described in U.S. Pat. Nos. 4,414,372; 4,417,034; 4,508,880; 4,524,196; 4,581,428; 4,588,795; 4,598,161; 4,605,716; 4,622,372; 4,656,233; 4,659,782; 4,659,783; 4,681,918; 4,695,607; and 4,711,942; and in commonly assigned United States patent applications Ser. Nos. 912,117 and 912,118 filed Sept. 29, 1986; 934,826 filed Nov. 25, 1986; 004,831 filed Jan. 13, 1987; 007,758 filed Jan. 27, 1987; and 048,958 filed May 19, 1987. These patents and patent applications disclose processes for polymerizing an acrylic or maleimide monomer to a "living" polymer in the presence of
(i) an initiator having at least one initiating site and which is a tetracoordinate organo(Si, Sn or Ge) compound, including such a compound having at least one oxygen, nitrogen or sulfur atom attached to Si, Sn or Ge; and
(ii) a co-catalyst which is a source of fluoride, bifluoride, cyanide or azide ions or a suitable Lewis acid, Lewis base or selected oxyanion.
The aforesaid patents and patent applications also disclose capped, block, star and graft polymers prepared by GTP methods, and any of such polymers containing functional groups which are useful for further processing. Group Transfer Polymerization is further discussed in detail by Sogah et al. in Macromolecules, 20, 1473 (1987).
All of the aforesaid patents and patent applications employ initiators and catalysts (referred to also as co-catalysts) which are soluble to some extent in the polymerization solvent, if any, or in the monomers employed. It has until now been believed that such solubility was essential. The present invention provides an improved GTP process wherein the initiator or the catalyst is chemically attached (grafted) to an insoluble support material, thus facilitating separation and recovery of the "living" polymeric product and of the initiator or catalyst. In a preferred embodiment, the "living" polymer remains grafted to the support.
Use of catalysts or initiators which are supported on insoluble materials in synthetic reactions, including non-GTP polymerizations, are known. A. Akelah et al., Chem. Revs., 81, 557 (1981) review the application of functionalized polymers in organic synthesis. Functionalized polymers are defined as synthetic macromolecules to which are chemically bound functional groups which can be utilized as reagents, catalysts, etc. A wide variety of polymer-supported catalysts and their uses in organic synthesis are described. Ionic catalysts wherein the cation is chemically bound to a polymeric support, such as polystyrene, are disclosed; e.g. PS--(CH.sub.2).sub.n N (R).sub.2 R' X.sup.- wherein PS is polystyrene, n is 0 or 1-3, R and R' are hydrocarbyl and X can include F, Cl, Br, OCN and OH.
Hellstern et al , Polymer Preprints (Am. Chem. Soc., Div. Poly. Chem.),28 [2], 328 (1987)) disclose the preparation of a soluble methacrylate-functional macromonomer by reacting poly(dimethyl siloxane) with 3-methacryloxypropyldimethylchlorosilane, and conversion of the macromonomer to a graft copolymer by GTP employing a silyl ketene acetal initiator and an acetate catalyst.
G. Cainelli et al., Synthesis Communications, November, 723 (1975) disclose anion exchange resins which are useful as catalysts in many organic reactions. The resins contain quaternary ammonium cations chemically bonded to a macroreticular resin such as Amberlite IRA-904; counter anions include oxyanions such as carboxylate.
T. Mukaiyama et al., Chemistry Letters (Japan), 1363 (1985) disclose aldol reactions of acetals and silyl enol ethers catalyzed by polystyrene-supported trityl perchlorate, forming beta-keto ethers.
J. F. W. Keana et al., J. Org. Chem., 51(10), 1641 (1986) describe the immobilization of biologically active materials, such as cholesterol or 1-adamantanamine, by reaction with chlorocarbonate-derivatized silica gel.
M. A. Askarov et al., Vysokomol. Soedin., Ser. B., 15(9), 650 (1973); Chem. Abstracts 80(16):83714m disclose initiation of vinyl monomer polymerization, including methyl methacrylate, by heating in water in the presence of trialkylammonium salts of chlorinated styrene-divinylbenzene copolymers.
U.S. Pat. No. 4,232,141 discloses polymerization of vinyl chloride in aqueous medium using a water-insoluble polymerization initiator; the initiator is well dispersed in the polymerization medium.
Immobilization of biologically active materials, such as enzymes, on insoluble macromolecular supports is well known.
International Publication No. WO 86/01514 discloses solid phase synthesis of oligonucleotides wherein the first monomer unit is attached to the solid phase by a urethane bridge.
U.S. Pat. No. 4,574,060 discloses the dimerization of acrylonitrile to 1,4-dicyano-1-butene using a cross-linked polystyrene bound diarylphosphinite catalyst of the formula Polymer--C.sub.6 H.sub.4 --P(OR)Ar wherein Polymer is polystyrene crosslinked with 1% of divinylbenzene, R is alkyl and Ar is substituted phenyl.
The surface properties of polymeric materials are important in many industrial, electronic, biotechnology and medical applications, particularly those applications depending on molecular interactions at the interface between the surrounding media and the bulk polymer.
The bulk properties of polymers are known to influence their mechanical properties and molecular structure. Often, however, the average bulk chemical properties are unsuited to the desired surface requirements for specific applications. For example, the molecular composition required for structural strength may differ from that required for biocompatibility, dye retention, chemical reactivity or inertness. Furthermore, surface chemical properties may be changed by external factors such as orientation, oxidation, contamination and fabrication.
Several coating and grafting techniques have been developed in the art for selective modification of surface properties, including:
Ionizing Radiation Grafting (e.g. UV, gamma ray, electron beam);
Chemical Grafting (e.g. ceric ion reactions with --OH);
Peroxide Reactions (e.g. thermal and chemical activation);
Active Vapor Reactions (e.g. RF and microwave plasma);
Anionic Grafting (e.g. metal halogen formation);
Cationic Grafting (e.g. aluminum alkyl initiated reactions);
Ziegler--Natta Reactions; and
Polycondensation Coupling Methods. Each of the above methods can provide surfaces which differ substantially from the bulk polymer in both chemistry and morphology. However, each method is limited in its capacity to tailor surface properties for a specific application, by (i) the nature of the polymerization reaction and the inherent control provided therein; and/or (ii) the solubility and molecular mobility (fluidity) of the bulk polymer.
The art methods do not permit sufficient control over graft polymer structure, composition and functionality for many important uses. Moreover, the art grafting methods normally require substantial polymer fluidity, which makes it difficult or impossible to graft molecules thereto with the required degree of molecular orientation.
To maintain control over the spatial orientation of graft polymers, it is important that the grafting method provide for covalent coupling of graft material to a rigid support. Furthermore, the grafting method should function on insoluble and highly crosslinked bulk polymers which do not swell or solubilize in the presence of monomers, solvents, and/or reagents used in the grafting process or in use. With many art grafting methods, especially radiation grafting, a fluid bulk phase is essential to insure monomer contact with free radicals. As radical formation is mass dependent, radical concentration at the surface tends to be low, and hence retention of molecular orientation is poor.
An object of this invention is to provide additional techniques for carrying out Group Transfer Polymerization. Another object is to provide grafting technology which affords improved control over, and means of manipulating, the molecular structure, composition, orientation and surface properties of the resultant grafted polymer.